What would we do without bees? They give us honey and pollinate hundreds of staple food crops throughout the world. Now it seems that the insects may play yet another role in keeping us well fed: Their buzz protects crops and other plants from caterpillar damage.
Caterpillars destroy plants by feeding on leaves, flowers, and fruits. But they have a predator of their own: the wasp. To defend itself, the caterpillar has developed sensory hairs that "feel" the air vibrations caused by the beating of wasp wings. If a wasp approaches, the caterpillar stops moving or drops off the plant for safety. Jürgen Tautz, a biologist at the University of Würzburg in Germany, wondered whether bees, whose wings beat with a similar frequency to those of wasps, would have a similar effect.
Tautz and his Würzburg colleague Michael Rostás built two cube-shaped tents in the botanical garden of their university, each enclosing 10 bell pepper plants. They then placed about 10 beet armyworm caterpillars (Spodoptera exigua), a notorious crop pest, on each plant. One tent had a window connected to a beehive, and feeders filled with a sugar solution attracted bees inside. The second tent was closed to the outside world. After about 2 weeks, Tautz and Rostás collected the leaves from the bell pepper plants.
Bees do indeed protect crops from caterpillars, according to findings reported online today in Current Biology. Bell pepper leaves in the tent frequented by bees experienced one-third of the leaf damage as those in the control tent. Similar results were obtained from a second experiment with soybean plants. When a caterpillar drops off a plant in response to a bee's buzz, it's wasting precious feeding time, says Tautz. But ignoring a hovering wasp can be deadly, so it pays to play it safe.
The scientists say that the discovery highlights the need to protect honey bees, which are disappearing in record numbers. "While the study was small, the results were convincing," says ecologist Thomas Ings of the University of London, Queen Mary, a specialist in pollinator behavior. Tautz also sees a role for the bees in a more environmentally friendly type of pest control: Seeding crop fields with a few more flowers should attract more bees--and fewer caterpillars--to a field, he says.